In the latest 2.79 daily build, is it possible to convert the Bevel node's RGB normal maps to BW edge highlighters?
Final result and node setup:



After many tryouts with complicated setups it seems that this effect could be easily achieved by using Vector Math > Cross Product from Bevel > Normal output and Texture Coordinates > Normals. 

After this the most efficient way is to use Color Ramp to change softness/sharpness of the edges.